Convert image to 1 bpp bitmap in .net compact framework

Question

I have an image of a signature I am trying to save as 1 bpp bitmap to save file space. The full .NET Framework has the enum PixelFormat.Format1bppIndexed, but

Answer 1

I had to do this in the past for generating black & white reports printed via Bluetooth (color or greyscale images were too large for the printer's buffer). Turned out I had to create the images using native code.

Here's a snippet:

private void CreateUnmanagedResources()
{
    // for safety, clean up anything that was already allocated
    ReleaseUnmanagedResources();

    bih = new BITMAPINFOHEADER();
    bih.biBitCount = 1;
    bih.biClrImportant = 0;
    bih.biClrUsed = 0;
    bih.biCompression = 0;
    bih.biHeight = m_cy;
    bih.biPlanes = 1;
    bih.biSize = (uint)(Marshal.SizeOf(typeof(BITMAPINFOHEADER)) - 8); 
    bih.biSizeImage = 0;
    bih.biWidth = m_cx;
    bih.biXPelsPerMeter = 0;
    bih.biYPelsPerMeter = 0;
    bih.clr2 = 0xffffff;
    bih.clr1 = 0x0;

    hDC = Win32.CreateCompatibleDC(IntPtr.Zero);
    pBits = IntPtr.Zero;
    hBitmap = Win32.CreateDIBSection(hDC, bih, 1, ref pBits, IntPtr.Zero, 0);
    hbmOld = Win32.SelectObject(hDC, hBitmap);
}

private void ReleaseUnmanagedResources()
{
    if (hbmOld != IntPtr.Zero)
        Win32.SelectObject(hDC, hbmOld);

    if(hBitmap != IntPtr.Zero)
        Win32.DeleteObject(hBitmap);

    if (hDC != IntPtr.Zero)
        Win32.DeleteDC(hDC);
}

I then used Graphics.FromHdc to get a managed graphics object that I could paint the report onto.

I did saving with a BinaryWriter, but that was in CF 1.0 days when the Bitmap class didn't have a Save, so you're free and clear there.